If one you own or plan on buying appears on those lists, you're set. In iOS, the "Print" command in the sharing-actions menu should work as long as your device is on the same Wi-Fi network as your printer - although not all apps support AirPrint equally. In Android, you'll need to add your printer to your CloudPrint settings and install one of a handful of apps to enable remote printing.

My own three-year-old Canon Wi-Fi printer-scanner doesn't grace either Apple or Google's databases of supported hardware. But that exclusion wound up not being a problem.

How? Canon - along with HP, Epson, and Kodak, to name a few - ships its own iOS and Android printing apps. Try searching the App Store or the Play Store for "[your printer manufacturer's name] print," and you may be pleasantly surprised

I tried Canon's free Easy Photo-Print on an iPad mini and a Galaxy Nexus Android phone; on the tablet, it detected the printer almost instantly, while on the latter I had to tap an extra button or two to have it perform the same task. Both printed a photo without complaint.

That app did not provide all the printing options I'd have on a desktop - for instance, it appears incapable of printing an e-mail or a Web page on either device, and I could only get it to offer to print a downloaded PDF on the iPad - but it seems sufficient for my purposes.

(But I print things a lot less than I once did. My single biggest use of this printer-scanner now is probably remotely depositing checks.)

If you only need to print what's on your current screen, you have a couple of simpler options.

For a full-resolution copy, you can take a screen shot (in iOS, hold down the power and home buttons; in the current version of Android, press the power and volume-down buttons for a second). Apple's PhotoStream should have it land in your iPhoto library or Windows' Pictures library within moments. On an Android device, the Google+ app will also automatically upload it, or you can use the share menu's Bluetooth option to beam it over to any computer equipped with this wireless technology.

If you don't need to capture every detail, just put the device screen-down in a color copier (note that most printer-scanners can also function offline as copiers), run off a print and call it a day.

Tip: "Long press" lives on in Android and iOS

If you're looking for a command that you just know should be somewhere in a phone or tablet app, try tapping and holding on the screen or whatever part of it you're trying to work with - a Web link or an e-mail message, for instance.

You may see nothing happen, or you may see a menu pop up with relevant commands. This "long press" is the rough equivalent of the right-click contextual menus in most Windows and Mac apps. If you know such a thing exists, it can represent a convenient shortcut; if not, it can seem an infuriating exercise in burying important controls.

Developers, however, haven't all gotten the memo. Many Android apps still hide some commands behind a long press of the screen, and a few iOS ones lean on this crutch of an interface too (for instance, it's faster to switch accounts in Twitter's iPad app with a long press of its "Me" icon). So you may need to keep trying this option when you get stuck in an app for a while longer.